There are complex rules for determining what is or is not a rebellion, but one thing to consider is whether it is an uprising by a non-legally-constituted body against the legal authority of the country ie the lawful government. In Ireland this was at the time the British Government. Normally war has to be declared by one government to another, or an act undertaken eg invasion which is a casus belli (a recognised cause of war).

In Spain the government of King Joseph was French; however, it was widely regarded as not lawful, certainly by the Spanish, and obviously by the British, since they fought against it. The Spanish formed an alternative government - the Juntas. And the Spanish monarch was still in existence. This is no doubt why the Portuguese court fled to Brazil; they formed a government in exile, so no-one could say that there was a vacuum in government or that the French could be the authority.

Cheers

C